<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>(P)_{title}</title>
    <style>
        /* 选择器{}*/
        /* 标签选择器 = <命名> */
        P {
            color: red;
        }
        /* <>=所有都生效css */
    </style>
</head>
<body>
    <P>Hello World</P>
    <P>demo_Hello-World_color</P>
    
</body>
</html>